Vaccines protect against a wide variety of infectious diseases. Many modern vaccines are therefore made from protective antigens of the pathogen, which are isolated by molecular cloning and purified. These vaccines are known as ‘subunit vaccines’. The development of subunit vaccines has been the focus of considerable research in recent years. The emergence of new pathogens and the growth of antibiotic resistance have created a need to develop new vaccines and to identify further candidate molecules useful in the development of subunit vaccines. Likewise the discovery of novel vaccine antigens from genomic and proteomic studies is enabling the development of new subunit vaccine candidates, particularly against bacterial pathogens. However, although subunit vaccines tend to avoid the side effects of killed or attenuated pathogen vaccines, their ‘pure’ status means that subunit vaccines do not always have adequate immunogenicity to confer protection.
An approach to improve the efficacy of vaccine compositions is to provide multivalent vaccines comprising dominant antigens that provoke both a B cell and T cell response thereby mounting a more rigorous immune response in the subject receiving the vaccine. A typical multivalent vaccine might be a whole cell vaccine comprising multiple antigenic molecules. For example the Bacillus Calmette Guerin [“BCG”] vaccine includes an attenuated Mycobacterium bovis strain that provokes protective immunity in humans. For many pathogens chemical or heat inactivation while it may give rise to vaccine immunogens that confer protective immunity also gives rise to side effects such as fever and injection site reactions. In the case of bacteria, inactivated organisms tend to be so toxic that side effects have limited the application of such crude vaccine immunogens and therefore vaccine development has lagged behind drug-development. Moreover, effective vaccine development using whole cell inactivated organisms suffers from problems of epitope masking, immunodominance, low antigen concentration and antigen redundancy.
Currently there is no effective vaccination procedure to prevent or treat Staphylococcus aureus infection. S. aureus is a bacterium whose normal habitat is the epithelial lining of the nose in about 20-40% of normal healthy people and is also commonly found on people's skin usually without causing harm. However, in certain circumstances, particularly when skin is damaged, this pathogen can cause infection. This is a particular problem in hospitals where patients may have surgical procedures and/or be taking immunosuppressive drugs. These patients are much more vulnerable to infection with S. aureus because of the treatment they have received. Antibiotic resistant strains of S. aureus have arisen since their wide spread use in controlling microbial infection. Methicillin resistant strains are prevalent and many of these resistant strains are also resistant to several other antibiotics.
S. aureus is therefore a major human pathogen capable of causing a wide range of diseases some of which are life threatening diseases including septicaemia, endocarditis, arthritis and toxic shock. This ability is determined by the versatility of the organism and its arsenal of components involved in virulence. At the onset of infection, and as it progresses, the needs and environment of the organism changes and this is mirrored by a corresponding alteration in the virulence determinants which S. aureus produces. At the beginning of infection it is important for the pathogen to adhere to host tissues and so a large repertoire of cell surface associated attachment proteins are made. The pathogen also has the ability to evade host defenses by the production of factors that reduce phagocytosis or interfere with the ability of the cells to be recognised by circulating antibodies.
There is therefore a continuing need to identify staphylococcal antigens that are protective and can be used in multivalent vaccines. The combinations may be used in combination with non-protein immunogenic molecules such as polysaccharide antigens and anti-bacterial agents to provide a treatment regimen for control of staphylococcal infection. It is also within the scope of this disclosure to modify the treatment regimen to immunize subjects with a series of temporally separated administrations as an alternative to the administration of a single vaccine comprising multiple antigens.